Storm shelters are in the news so I'll attempt a few:
Dig a 6' by 8' rectangle trench that is 18" deep. Pour concrete 20" high. S
tick stainless-steel angles vertical in the concrete every 24". And these a
ngles could be 2" by 2" by 1/8" and 6' high above the ground. Turn the angl
es for a flat surface facing out and for a corner at the corners. Have the
tops of the angles make a slight slope front to rear. Overlap the tops of t
he angles with horizontal angles across the building width and bolt them to
gether with 1/4" stainless steel bolts and nuts. Attach stainless-steel she
et that is 0.10" thickness to the angles with stainless-steel bolts and nut
s. This is front, sides, back, and top. Except leave the front open for a 4
' door design and that could be either a swinging door or a sliding door. D
o a final roofing over the sheet gaps with 0.015" thickness stainless-steel
sheet that is overlapped and attached to the building sides with stainless
-steel metal and wood screws.
Optional: Poor a 4" thick concrete floor. Insulate the inside and attach th
in paneling with stainless-steel metal and wood screws. Attach 1" x 5" ceda
r boards to the outsides of the building with stainless-steel metal and woo
Of course buy the stainless-steel from a regional steel distributor.
Or for a building with rounded corners pour concrete walls into forms and a
ttach a roof as previously described to stainless-steel angles sticking up
from the walls.
The reason for all the stainless-steel ? Well, 300 series stainless-steel w
ill never rust or corrode and thus a seal from the outside weather doesn't
have to be perfect.
Then the advantage of this storm shelter is that it is also a tool shed or
lawn mower shed.
Perhaps easier, pre-cast concrete pieces are available to make a manhole in
the ground. However, the manhole needs a pipe laid for drainage in additio
n to setting the manhole six feet in the ground